A role of Na+, K+ -ATPase in spatial memory deficits and inflammatory/oxidative stress after recurrent concussion in adolescent rats.

Sports-related concussions are particularly common during adolescence, and there is insufficient knowledge about how recurrent concussions in this phase of life alter the metabolism of essential structures for memory in adulthood. In this sense, our experimental data revealed that seven recurrent concussions (RC) in 35-day-old rats decreased short-term and long-term memory in the object recognition test (ORT) 30 days after injury. The RC protocol did not alter motor and anxious behavior and the immunoreactivity of brain-derived neurotrophic factor (BDNF) in the cerebral cortex. Recurrent concussions induced the inflammatory/oxidative stress characterized here by increased glial fibrillary acidic protein (GFAP), interleukin 1ß (IL 1ß), 4-hydroxynonenal (4 HNE), protein carbonyl immunoreactivity, and 2',7'-dichlorofluorescein diacetate oxidation (DCFH) levels and lower total antioxidant capacity (TAC). Inhibited Na+,K+-ATPase activity (specifically isoform α2/3) followed by Km (Michaelis-Menten constant) for increased ATP levels and decreased immunodetection of alpha subunit of this enzyme, suggesting that cognitive impairment after RC is caused by the inability of surviving neurons to maintain ionic gradients in selected targets to inflammatory/oxidative damage, such as Na,K-ATPase activity.

Contrasting effects of Na+, K+-ATPase activation on seizure activity in acute versus chronic models.

Epilepsy is a life-shortening brain disorder affecting approximately 1% of the worldwide population. Most epilepsy patients are refractory to currently available antiepileptic drugs (AEDs). Knowledge about the mechanisms underlying seizure activity and probing for new AEDs is fundamental to the discovery of new therapeutic strategies. Brain Na(+), K(+)-ATPase activity contributes to the maintenance of the electrochemical gradients underlying neuronal resting and action potentials as well as the uptake and release of neurotransmitters. Accordingly, a decrease of Na(+), K(+)-ATPase increases neuronal excitability and may predispose to appearing of seizure activity. In the present study, we tested the hypothesis that activation of Na(+), K(+)-ATPase activity with a specific antibody (DRRSAb) raised against a regulatory site in the α subunit would decrease seizure susceptibility. We found that incubation of hippocampal homogenates with DRRSAb (1 µM) increased total and α1 Na(+), K(+)-ATPase activities. A higher concentration (3 µM) increased total, α1 and α2/α3 Na(+), K(+)-ATPase activities. Intrahippocampal injection of DRRSAb decreased the susceptibility of post status epilepticus animals to pentylenetetrazol (PTZ)-induced myoclonic seizures. In contrast, administration of DRRSAb into the hippocampus of naïve animals facilitated the appearance of PTZ-induced seizures. Quantitative analysis of hippocampal electroencephalography (EEG) recordings revealed that DRRSAb increased the percentage of total power contributed by the delta frequency band (0-3 Hz) to a large irregular amplitude pattern of hippocampal EEG. On the other hand, we found no DRRSAb-induced changes regarding the theta functional state. Further studies are necessary to define the potential of Na(+), K(+)-ATPase activation as a new therapeutic approach for seizure disorders.

Involvement of oxidative stress in subacute toxicity induced by fumonisin B1 in broiler chicks.

Fumonisin B1 (FB1) is a mycotoxin produced by Fusarium spp. It has been reported to be a potential cause of liver cancer in rats and esophageal cancer in humans. The underlying mechanisms of FB1 toxicity are thought to be related to the inhibition of ceramide synthase, causing an accumulation of sphingosine (SO) and sphinganine (SA), which in turn may cause tissue functional impairment and the development of oxidative stress. Therefore, in this study, we investigate the effects of an FB1-contaminated diet on markers of oxidative stress in chick liver. A total of 24 male broiler chicks (Cobb 500) were fed a standard control diet or a diet contaminated with FB1 (100mg/kg) for 21 days, starting on postnatal day one. The feed and animals were weighed on days 0, 7, 14 and 21 to estimate the feed conversion ratio, and at 21 days, the liver weight and liver relative weight were determined. At the end of the experiment, samples of blood and liver were collected. The blood was used to quantify the SA/SO ratio, and the liver was used to determine the activity of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST); ascorbic acid levels (VitC), non-protein thiol (NPSH) levels and TBARS content were also determined. The FB1 diet increased the liver weight, liver relative weight, feed conversion and SA/SO ratio. Furthermore, hepatic TBARS levels, Vit C content and CAT activity were also increased. Conversely, the activities of SOD, GST and NPSH levels, in the liver were not altered by the mycotoxin-contaminated diet. In summary, we showed that subacute exposure of broiler chicks to FB1 induced liver oxidative stress concomitantly with SA/SO accumulation.

Modulation of pentylenetetrazol-induced seizures by prostaglandin E2 receptors.

There is evidence that prostaglandin E2 (PGE2) facilitates the seizures induced by pentylenetetrazol (PTZ), but the role of PGE2 receptors (EPs) in the development of seizures has not been evaluated to date. In the current study we investigated whether selective EP ligands alter PTZ-induced seizures in adult male Wistar rats by electrographic methods. Selective antagonists for EP1 (SC-19220, 10 nmol, i.c.v.), EP3 (L-826266, 1 nmol, i.c.v.) and EP4 (L-161982, 750 pmol, i.c.v.) receptors, and the selective EP2 agonist butaprost (100 pmol, i.c.v.) increased the latency for clonic and generalized tonic-clonic seizures induced by PTZ. These data constitute pharmacological evidence supporting a role for EPs in the seizures induced by PTZ. Although more studies are necessary to fully evaluate the anticonvulsant role these compounds and their use in the clinics, EP ligands may represent new targets for drug development for convulsive disorders.

Creatine protects against the convulsive behavior and lactate production elicited by the intrastriatal injection of methylmalonate.

Methylmalonic acidemias are metabolic disorders caused by a severe deficiency of methylmalonyl-CoA mutase activity, which are characterized by neurological dysfunction, including convulsions. It has been reported that the accumulating metabolite, L-methylmalonic acid (MMA), inhibits succinate dehydrogenase leading to ATP depletion in vitro, and that the intrastriatal injection of MMA induces convulsions through secondary NMDA receptor stimulation. In this study we investigated the effect of creatine (1.2, 3.6 and 12.0 mg/kg, (i.p.), [DOSAGE ERROR CORRECTED] succinate (1.5 micromol/striatum) and MK-801 (3 nmol/striatum) on the convulsions and on the striatal lactate increase induced by MMA (4.5 micromol/striatum) in rats. The effect of creatine on the striatal phosphocreatine content and on MMA-induced phosphocreatine depletion was also evaluated. Creatine, succinate and MK-801 pretreatment decreased the number and duration of convulsive episodes and the lactate increase elicited by MMA. Creatine, but not succinate, prevented the convulsions and the lactate increase induced by the direct stimulation of NMDA receptors. Acute creatine administration increased the total striatal phosphocreatine content and prevented MMA-induced phosphocreatine depletion. Our results suggest that MMA increases lactate production through secondary NMDA receptor activation, and it is proposed that the anticonvulsant effect of creatine against MMA-induced convulsions may be due to an increase in the phosphocreatine content available for metabolic purposes.